ISBN 9783868538892

Alexandra A. MankaPhase Transitions of Water - From Vapor to Supercooled Droplets to Ice

165 Seiten, Dissertation Universität Köln (2011), Softcover, A5

Zusammenfassung / Abstract

Nucleation, condensation and freezing of water are of considerable interest in several natural and industrial processes. The rates at which the phase transitions occur, the degree to which pure water can be supercooled, and the solid phases that form are all fundamentally interesting questions with strong atmospheric relevance. In this work, homogeneous nucleation of condensing water (H2O) vapor was studied using three different devices: a Laminar Flow Diffusion Chamber (LFDC), a Free Expansion Chamber (FEC) and a Supersonic Nozzle (SSN). Furthermore, in the SSN the subsequent freezing of the formed water nano-droplets was characterized by use of Small Angle X-ray Scattering (SAXS) and Fourier Transform Infrared spectroscopy (FTIR). FTIR spectroscopy revealed the first strikingly clear evidence of freezing of highly sub-cooled H2O nano-droplets in the nozzle at temperatures below ~212 K – a temperature that is well below the homogeneous freezing limit for bulk water.